Numerous medical procedures require the use of a sheathed needle, that when unsheathed, is used to pierce tissue at a certain depth for delivery of a fluid. For example, Botulinum toxin (trade name Botox®) may be injected into a bladder wall to treat an over-active bladder. Other treatments using sheath-covered needles include those in the field of urology, such as vesicoureteral reflux (VUR) as well as those in the field of gastrointestinal endoscopy such as injection into the gastrointestinal mucosa.
The needle is sheathed as it is moved to the injection location to protect the patient, endoscope, cystoscope, or other medical device from accidental piercing whilst the needle is being positioned over the target injection site. The sheath is then retracted exposing a portion of the needle. However, current devices are unable to provide for precise needle exposure which is often desired for delivery of a fluid into the area to be treated. The farther away the controlling handle is from the tip, the more pronounced this inability to accurately control component movement becomes, especially when the device is held in a curved orientation. Thus, although a user believes s/he is unsheathing, for example, 2 mm of the needle, the actual amount of needle unsheathed is not 2 mm when the device is held in a curved orientation. Instead, the unsheathed portion of the needle may be greater than or less than that desired due to material tolerances and material flexibility—but those tolerances and flexibility are often desired to properly position the device over the target injection site.